Download Nuclear cardiology in the clinical setting

Nuclear cardiology in the clinical setting
Nuclear cardiology has made great strides in the past three decades.
C D Libhaber, MD, FCNP
Department of Nuclear Medicine and Molecular Imaging, University of the Witwatersrand, Johannesburg, South Africa
Corresponding author: C D Libhaber ([email protected])
During the past three decades, the most rapidly growing areas of
nuclear cardiology have been stress myocardial perfusion imaging
single photon emission computed tomography (MPI SPECT) and
positron emission tomography (PET) for the diagnosis and prognosis
of patients with known or suspected coronary artery disease (CAD).
A stress ECG has a relatively low sensitivity and specificity. MPI is both
more sensitive and specific than an exercise ECG for diagnosing CAD.
Maximal benefit is observed in patients with intermediate probability
of the disease, and in those with non-diagnostic ECGs.
Uses of MPI include:
• diagnosis of CAD
• identification of the site of ischaemia
• quantification of the extent and severity of impaired coronary
flow reserve
• evaluation of acute ischaemic syndromes
• evaluation before surgery
• prognostic assessment of CAD patients
• assessment of tissue viability.
MPI is indicated to exclude or diagnose CAD in patients with suspected
CAD, and as a screening test in those with intermediate CAD or at high
risk of CAD. The latter includes patients with familial hyperlipidaemia,
type II diabetes mellitus, family history of CAD, as well as those with
atypical symptoms of ischaemic heart disease undergoing surgery and
who are at high risk of developing peri- or postoperative cardiovascular
events, e.g. those with peripheral vascular disease, aortic aneurysm,
acute chest pain and the elderly.
In patients with CAD with congestive
heart failure, it is important to identify
viable myocardium.
Patients with a high probability of developing coronary heart disease
require imaging to help in the planning of appropriate management
rather than for diagnosis. MPI is particularly valuable to confirm
silent myocardial ischaemia or infarction.
Multiple non-coronary causes of ST-segment depression that can
render the stress ECG uninterpretable are:
• digitalis
• severe hypertension
• severe aortic stenosis
• anaemia
• severe hypoxia
Fig 1. A normal myocardial perfusion scan (MPI). The upper row Fig. 2. Myocardial perfusion imaging (MPI), showing severe ischaemia
shows the stress images and the bottom row the rest images, in the in the apical and apical-anterior segments.
short axis, long axis vertical and long axis horizontal views.
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left ventricular hypertrophy
glucose load
hypokalaemia
mitral valve prolapse
IV conduction disturbance
supraventricular tachyarrhythmias
cardiomyopathy
sudden excessive exercise
hyperventilation
severe volume or pressure overload.
In the abovementioned cases, MPI can
contribute in clarifying the presence or
absence of ischaemia.
Patients with a
high probability of
developing coronary
heart disease require
imaging to help in the
planning of appropriate
management rather than
for diagnosis.
In patients with confirmed CAD, MPI is
indicated in:
• Evaluation of the functional significance of
a coronary lesion. The extent and severity of
the stress perfusion defect is closely related
to subsequent cardiac events. It is therefore
important to determine the size, severity and
reversibility of a stress-induced perfusion
defect. Functional criteria provide more
accurate characterisation of stenosis severity
than angiographic criteria. The presence of
an angiographic lesion does not necessarily
mean that it is responsible for the patient’s
symptoms.
• Risk stratification and prognosis evaluation.
• Detection of ‘high-risk’ CAD.
• Post-infarction risk stratification. Detection
of ischaemia, either at the site of injury or in
a different region, detection of myocardial
viability in the infarcted region, and flowfunction relationship (from gated SPECT).
• Deciding on long-term medical management
versus revascularisation in patients with stable
angina.
• D ete c t ion of restenosis af ter
revascularisation, percutaneous transluminal
coronary angioplasty (PTCA), stents or
coronary artery bypass graft (CABG).
• Detection of residual ischaemia while
planning multiple PTCAs.
• Post-CABG evaluation in suspected graft
occlusion or for routine assessment.
• Thallium-201, and technetium-99m radiolabelled lipophilic compounds such as
sestamibi and tetrofosmin – most commonly
used for MPI SPECT.
viable myocardium. Ventricular function
and symptoms may improve with
revascularisation therapy in patients
with significant hibernating or stunned
myocardial tissue. In addition, patients
with viable myocardium are at greater
risk of hard events than those without
viability when treated medically and not
referred for revascularisation. MPI SPECT
with thallium-201, Tc-99m sestamibi or
tetrafosmin and PET imaging with F-18
flourodeoxyglucose (FDG) have an essential
role in localising viable myocardium.[16-19]
There are multiple contraindications to a
physical stress test:
• poor motivation to exercise
• poor exercise capacity due to non-cardiac
endpoints (such as fatigue or shortness
of breath)
• beta-blocking drugs that limit heart rate
response
• left bundle-branch block
• fewer than 5 days after a myocardial
infarction
• peripheral arteriosclerotic vascular disease
• disabling arthritis
• history of stroke
• orthopaedic problems (e.g. low back
pain)
• chronic pulmonary disease
• amputation of an extremity.
A stress ECG has a
relatively low sensitivity
and specificity. MPI is
both more sensitive
and more specific than
exercise ECG for the
diagnosis of CAD.
In these cases, exercise can be replaced by
pharmacological stress by administering
vasodilators, e.g. adenosine or dipyridamole,
or inotropic agents, e.g. dobutamine.
The sensitivity and specificity of the
pharmacological and physical stress tests
are equivalent.
Currently, the clinical approach is based on
identifying patients who are at risk for cardiac
death and non-fatal myocardial infarction
rather than those with anatomical coronary
disease. MPI therefore plays a fundamental
part in the diagnosis and risk stratification of
these patients.[2]
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According to the American Society of
Nuclear Cardiology, the overall risk of hard
adverse events (death or non-fatal myocardial
infarction) in an individual with a normal
perfusion scan is <1% for a period of 12 months,
independent of age, gender, symptoms, history
of CAD, presence of CAD, isotope or imaging
technique used (Fig. 1).[1] If the perfusion scan
is abnormal, the risk of adverse events increases
in proportion to the affected area.[2-12]
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Fixed and reversible perfusion defects can
predict hard events. However, patients with
extensive stress-induced ischaemia are at
higher risk (Fig. 2).[3-6, 8, 9, 11, 13-15]
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Post-stress left ventricular ejction fraction
(LVEF), as measured by gated SPECT,
provides significant information in addition
to the extent and severity of perfusion defects
in the prediction of cardiac death.[10]
In patients with CAD and congestive
heart failure, it is important to identify
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Summary
• A stress ECG, with its relatively low sensitivity and specificity, may not be sufficient to
evaluate patients with known or suspected ischaemic heart disease.
• MPI SPECT is both more sensitive and specific than a stress ECG in the diagnosis and risk
stratification of patients with significant CAD and may act as a gatekeeper for coronary
angiography.
• There is extensive literature to show that patients with normal MPI are at very low risk of
hard cardiac events (death or non-fatal myocardial infarction) for 1 year and even 2 years
after the test. However, the risk increases linearly with the degree of ischaemia.
• Post-stress LVEF provides significant information on the extent and severity of the
perfusion defect on risk prediction. In patients with ischaemic heart disease and congestive
heart failure, MPI SPECT is an extremely valuable tool to identify and quantify viable
myocardial tissue.
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